title: Light polymerization during cavity filling: effect of 'exposure reciprocity law' and the resulted shrinkage forces on restoration margins.
abstract: OBJECTIVE
  To evaluate shrinkage development and marginal integrity of a micro hybrid restorative composite as a function of irradiance.
  
  
  METHODS
  Linear displacement and shrinkage were measured with custom-made devices for irradiances of 100, 200, 400, 800 and 1600 mW/cm(2) at a constant radiant exposure of 16 J/cm(2). Marginal adaptation (MA) of composite restorations performed with a self-etch adhesive (Syntac Classic, Ivoclar Vivadent) and a micro hybrid composite (Tetric, Ivoclar Vivadent) was evaluated before and after mechanical loading with 300,000 cycles at 70 N.
  
  
  RESULTS
  The highest percentage of MA was attained by the group light cured with an irradiance of 100 mW/cm(2) for 160 s. No significant differences were observed between the rest of the groups. Shrinkage development was similar in all groups.
  
  
  CONCLUSIONS
  For the material tested in this study, the reciprocal relationship between irradiance and time of exposure had no significant effect on restoration margins and shrinkage stress development within the range of 200-1600 mW/cm(2) with a constant radiant exposure of 16 J/cm(2).
authors.affiliation: Division of Cariology and Endodontics, School of Dental Medicine, University of Geneva , Switzerland. tissiana.bortolotto@unige.ch
authors.forename: Tissiana
authors.initials: T
authors.lastname: Bortolotto
authors.forename: Christel
authors.initials: C
authors.lastname: Dagon
authors.forename: Ivo
authors.initials: I
authors.lastname: Krejci
mesh_terms: D003793:Dental Restoration, Permanent; D008027:Light; D008855:Microscopy, Electron, Scanning; D011108:Polymers / Q000737:chemistry*
chemical_list: D011108:Polymers